1. Field of the Invention
The present invention relates to a device for resetting a servo actuator to its neutral position.
2. Description of the Related Art
Generally, a high degree of safety is required in an aircraft. Backup control systems are required so that, should one control system fail, other control systems can take over the impacted control function, thereby ensuring safe continuation of flight. However, there are cases where flight safety may be hampered if a control system develops a failure and is left in the condition at the time of the failure. When this occurs, there must be a capability to reset the failed control system to a neutral position, thereby not adversely affecting the flight.
Prior art control systems of this type have included a neutral position resetting device, which functions to reset a servo actuator for controlling an airfoil to a neutral position, when a failure in the actuator has developed. As shown in FIG. 17, this device comprises a servo actuator 3 whose rod 1 is linked with an airfoil 2. Servo control is effected by supply and discharge of oil pressure to and from the servo actuator 3 via an ordinary servo valve 4 and a switching valve 5. The quantity and direction of the oil pressure to be supplied to and discharged from the servo actuator are controlled by shifting a spool 6 of the servo control valve 4 with a motor 7, based on a signal sent from the cockpit. If it becomes impossible to control the servo actuator 3 because of a failure in the motor 7 or the servo control valve 4, the air foil 2 will be locked at a certain position which will adversely affect the flight. When such a situation develops, a solenoid valve 8 is actuated, causing switching valve 5 to be switched to the opposite direction. As a result, oil pressure supplied to or discharged from the servo actuator 3 via a control valve 9 acts to reset the piston rod 1 of the servo actuator 3 to a neutral position, thereby freeing the airfoil 2 from adverse affects.
In such a prior art neutral position resetting device, however, there are required two control systems, namely, a first hydraulic control system that leads from the servo control valve 4 to the servo actuator 3, and a second hydraulic control system that leads from the control valve 9 to the servo actuator 3. In addition, a switching valve 5 has to be interposed between the two systems for switching between them. This configuration has been disadvantageous in that the hydraulic circuit becomes complicated and the mechanism has to be large in scale and weight, resulting in higher production cost.